Method and apparatus for spinal interbody fusion including  fixation or locking plate

ABSTRACT

A spinal fusion implant has a parallelepiped main body with a rotatably mounted retention plate secured to its distal end. The distal retention plate has a first position co-planar with the main body and a second, deployed position normal to the plane of the main body. The distal retention plate is in the first position when the main body is inserted between adjacent vertebral bodies and is in the second position after the main body is inserted between adjacent vertebral bodies. In further embodiments, a proximal retention plate is permanently deployed in normal relation to the main body or both the distal and proximal retention plates are rotatably mounted and both are deployed co-planar to the main body before insertion and normal to the main body after insertion.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to surgical methods and apparatus in general, andmore particularly to surgical methods and apparatus for fusing spinalvertebral bodies.

2. Brief Description of the Related Art

Disc herniation is a condition in which a spinal disc bulges frombetween two vertebral bodies and impinges on adjacent nerves, therebycausing pain. In some cases, non-operative procedures such as bed rest,medication, lifestyle modifications, exercise, physical therapy,chiropractic care and steroid injections may suffice. However, in othercases, surgical intervention may be necessary. In cases where surgicalintervention is prescribed, spinal vertebral body fusion may bedesirable, i.e., the spine may have deteriorated so much that adjacentvertebral bodies must be fused together.

Spinal fixation is the current standard of care for surgically treatingdisc herniation in patients who have chronic pain and who have, or arelikely to develop, associated spinal instability. Spinal fixationprocedures are intended to relieve impingement on nerves by removing theportion of the disc or bone, or both, responsible for compressing theneural structures and destabilizing the spine. The excised disc or boneis replaced with one or more intervertebral implants, or spacers, placedbetween adjacent vertebral bodies. These implants stabilize the adjacentvertebral bodies relative to one another so that the two vertebralbodies can fuse together.

One problem with spinal fixation is that the surgeon must make incisionson both sides of the spine. This lengthens the time required to performan operation and it lengthens the patient's recovery time.

However, in view of the art considered as a whole at the time thepresent invention was made, it was not obvious to those of ordinaryskill in the art how conventional surgical procedures could be improved.

SUMMARY OF THE INVENTION

The long-standing but heretofore unfulfilled need for an improved spinalfusion implant is now met by a new, useful, and non-obvious invention.

The novel spinal fusion implant preferably includes a substantiallyparallelepiped body, hereinafter referred to as the main body, having apredetermined length, width, and thickness. The main body may also havea cylindrical or oval shape. In some embodiments, the upper and lowersurfaces may be oblique to one another so that a first side of thedevice may have more depth than a second side or a first end may havemore depth than a second end.

In a first embodiment, a retention plate is secured to a distal end ofthe main body. The retention plate has a first, undeployed position thatis co-planar with the main body and a second, deployed position that ismisaligned from the main body, allowing the retention plate to engage anadjacent vertebral body or bodies.

The main body has an operative position between adjacent vertebralbodies when in use. The length of the main body is sufficient to span adistance between opposing cortical portions of a vertebral body withoutextending substantially beyond the vertebral body when the body is inthe operative position. The thickness of the main body is substantiallythe same as a gap between opposing vertebral bodies in a spinal jointwhen the main body is in its operative position.

The retention plate is in its first, co-planar position when the mainbody is inserted between adjacent vertebral bodies and in its second,deployed position after the main body is inserted between adjacentvertebral bodies.

The spinal fusion implant is in the operative position after theinsertion. The retention plate holds the spinal fusion implant andadjacent vertebral bodies in a stable relationship to one another whenthe retention plate is deployed in its second, misaligned position.

In further embodiments, a second retention plate located on the proximalend of the main body is employed. The distal retention plate is mountedin co-planar relation to the main body at the time of insertion but theproximal retention plate may be in its deployed position at the time ofinsertion.

In some embodiments, a rod ties the distal and proximal retention platestogether so that after insertion, the proximal plate is deployed intoits operative position and the distal retention plate is conjointlydeployed therewith into its deployed position.

The novel spinal fusion implant is disposed between adjacent vertebralbodies to immobilize the affected segment and facilitate fusion betweenthe opposing vertebral bodies.

The spinal fusion implant can include gripping surfaces on the superiorand inferior faces of the main body. The spinal fusion implant may alsobe provided with convex superior and inferior surfaces. It can also betapered from the anterior to the posterior face. Moreover, the implantmay also include an insertion tool guide.

An important object of the invention is to provide a spinal fusionimplant that does not require incisions on both sides of a spine.

A more specific object is to provide a spinal fusion implant that isinserted from a proximal side of a spine and which has a retention platemounted on the distal end that is retracted into co-planar relation withthe implant main body when the implant is inserted and deployed into amisaligned relation to said implant main body after the insertion hasbeen completed.

Another object is to provide an implant where retention plates aremounted to both the distal and proximal ends of the implant body andwhere said retention plates are in their respective retracted positionsduring insertion and in their respective deployed configurations afterinsertion.

These and other important objects, advantages, and features of theinvention will become clear as this disclosure proceeds.

The invention accordingly comprises the features of construction,combination of elements, and arrangement of parts that will beexemplified in the disclosure set forth hereinafter and the scope of theinvention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be made to the following detailed disclosure, taken inconnection with the accompanying drawings, in which:

FIG. 1 a schematic view of a human spine;

FIG. 2 is a schematic view illustrating the novel spinal fusion implantinstalled in a disc space;

FIG. 3 is a perspective view of a first embodiment of the novel spinalfusion implant;

FIG. 4 is a side elevational view thereof;

FIG. 5 is a perspective view similar to FIG. 3 but with the distalretention plate in its deployed configuration;

FIG. 6 is a schematic view illustrating the spinal fusion implantinstalled with the retention plate deployed outside of the vertebralbody;

FIG. 7 is a schematic view illustrating the spinal fusion implantinstalled with the retention plate deployed inside of the vertebralbody;

FIG. 8 is a perspective view of a second embodiment;

FIG. 9 is a side elevational view thereof;

FIG. 10 is a perspective view of a third embodiment;

FIG. 11 is a perspective view of a fourth embodiment;

FIG. 12 is a perspective view of a fifth embodiment;

FIG. 13 is a top plan view of said fifth embodiment;

FIG. 14 is a perspective view of a sixth embodiment;

FIG. 15 is a top plan view of said sixth embodiment;

FIG. 16 is a perspective view of a seventh embodiment;

FIG. 17 is a perspective view similar to FIG. 16 but with the distalretention plate in its deployed configuration;

FIG. 18 is an end view of the seventh embodiment;

FIG. 19 is a perspective view of an eighth embodiment;

FIG. 20 is an end view of the eighth embodiment;

FIG. 21 is a perspective view of a ninth embodiment;

FIG. 22 is an end view of the ninth embodiment;

FIG. 23 is a top plan view of a tenth embodiment;

FIG. 24 is a side elevational view of the tenth embodiment;

FIG. 25 is an end view of the tenth embodiment;

FIG. 26 is a perspective view of a eleventh embodiment;

FIG. 27 is a top plan view of a twelfth embodiment;

FIG. 28 is a perspective view of a thirteen embodiment

FIG. 29 is a perspective view of a fourteenth embodiment;

FIG. 30 is a top plan view of the fourteenth embodiment;

FIG. 31 is a perspective view of a fifteenth embodiment;

FIG. 32 is a perspective view of a sixteenth embodiment;

FIG. 33 is a perspective view of the sixteenth embodiment with itsretention plates deployed;

FIG. 34 is a perspective view of a seventeenth embodiment;

FIG. 35 is a side elevational view of the seventeenth embodiment butwith the distal end retention plate in its deployed configuration;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 depicts a typical human spine S. Spine S includes a plurality ofvertebral bodies V separated by discs D. A spine may deteriorate so muchthat adjacent vertebral bodies must be fused together. The novel spinalfusion implant is disposed between contiguous vertebral bodies toimmobilize the affected segment of the spine and facilitate fusionbetween said contiguous vertebral bodies.

FIG. 2 depicts the novel spinal fusion implant installed in a discspace. More particularly, spinal fusion implant 5 is disposed betweentwo adjacent vertebral bodies V to stabilize those two vertebral bodiesrelative to one another and permit fusion of the same. The spine isprepared by removing some or all of the disc that resides in the spacewhich is to be occupied by spinal fusion implant 5. The disc space DS isprepared with a rongeur or other surgical instrument.

The novel structure effectively stabilizes the joint but permits theoccurrence of “micro-motion” between the opposing vertebral bodies,which is important for successful bone fusion.

Referring now to FIGS. 3-5, which depict the most basic embodiment ofspinal fusion implant 5, retention plate 35 is attached to main body 10by either central rod 55 or short shaft 195 (see FIG. 30). An adjustinginstrument may be inserted into instrument port 40 to slide retentionplate 35 laterally and deploy said retention plate.

Implant 5 includes a generally parallelepiped main body 10 having apredetermined length, width and depth. Although not preferred, acircular or oval configuration is also within the scope of thisinvention and the top and bottom surfaces of main body 10 may also beoblique to one another. Main body 10 has distal end 15, proximal end 20,smooth upper surface 25, and smooth lower surface 30. Distal retentionplate 35 is rotatably secured to main body 10 and main body 10 furtherincludes instrument port 40 for deploying retention plate 35. Uppersurface 25 and lower surface 30 are substantially parallel to oneanother but each surface is slightly convex as best understood inconnection with FIGS. 3 and 4.

Retention plate 35 overlies and is mounted to distal end 15. Retentionplate is in the non-rotated position depicted in FIGS. 3 and 4 when itis inserted between adjacent vertebrae. It is rotated into the FIG. 5position after such insertion. However, the rotation of retention plate35 need not be a full ninety degree (90°) rotation as depicted; anyrotation that prevents retraction of said main body 10 is sufficient.

Misalignment (at least some rotation) of distal retention plate 35 frommain body 10 limits motion in a multi-directional joint. Moreparticularly, the shape of main body 10 limits motion inflexion/extension, while retention plate 35 limits lateral bending. Thisconstruction eliminates the possibility of eccentric forces inducingmotion in the joint. Novel spinal fusion implant 5 may be manufacturedin a wide range of sizes in order to accommodate any size of discbetween the vertebral bodies.

The upper and lower surfaces 25, 35 of main body 10 may be formed withan inclined or non-parallel (oblique) configuration to provide thespinal fusion implant with an overall wedge shape in order to providespinal curvature where desired.

Novel spinal fusion implant 5 may be constructed out of substantiallyany biocompatible material, including bone, which has propertiesconsistent with the present invention including, but not limited to,ceramics, PEEK, stainless steel and titanium. Thus, the novel implantpermits a surgeon to select a spinal fusion implant having theappropriate size and composition for a given intervertebral fusion. Moreparticularly, the shape of main body 10 limits motion inflexion/extension, while retention plate 35 limits lateral bending. Thisconstruction eliminates the possibility of eccentric forces inducingmotion in the joint.

The configuration of spinal fusion implant 5 may be varied withoutdeparting from the scope of the present invention.

FIG. 7 is a schematic view depicting the spinal fusion implant installedwith the retention plate deployed inside of the vertebral body.

The second embodiment is depicted in FIGS. 8 and 9. It differs from thefirst embodiment because it adds distal spacer 60.

Retention plate 35 is attached to adjustable width spacer 60 whichslides laterally via an adjusting instrument inserted into instrumentport 40. This configuration provides more effective vertebral restingdue to the increased diameter of the adjustable width spacer 60.

The third embodiment is depicted in FIG. 10. It differs from the secondembodiment because it adds proximal retention plate 140 and a secondproximal spacer 60.

The fourth embodiment is depicted in FIG. 11. It adds a gripping surfaceto the respective inboard surfaces of distal retention plate 35 andproximal retention plate 140. No reference character is applied to saideasily seen gripping surfaces to avoid clutter of the drawings.

The fifth embodiment is depicted in FIGS. 12-13. This embodiment ofspinal fusion implant 5 includes rod 55 mounted coincident with thelongitudinal axis of symmetry of main body 10. Retention plate 35 ismounted at its center to the distal end of said rod but rod 55 does notprotrude through plate 35. Rotation of said rod about its longitudinalaxis of rotation is facilitated using proximal plate 140 and suchrotation effects conjoint rotation of said retention plate 35. Rotationof rod 55 also advances or retracts said rod relative to saidlongitudinal axis.

This fifth embodiment further includes adjustable width spacers 60 atits distal end 15 and proximal end 20. Both retention plates 35 and 140attach to rod 55 via said adjustable width spacer 60 as best depicted inFIGS. 12 and 13. Adjustable width spacer 60 has a larger diameter thanrod 55, thereby providing a more effective vertebral resting surface.

Two apertures, collectively denoted 50, are formed in this fourthembodiment of spinal fusion implant 5 and extend completelytherethrough. Apertures 50 preferably have a common shape and size andare disposed on opposite sides of and in equidistantly spaced relationto a transversely disposed imaginary line that bisects spinal fusionimplant 5.

This fifth embodiment also adds anti-retraction teeth 70 to upper andlower surfaces 25 and 30. Teeth 70 are swept back for insertion in aproximal-to-distal direction and such directional sweeping inhibitsdistal-to-proximal retraction.

Spinal fusion implant 5 is advanced horizontally, distal end first, intothe gap between the upper and lower vertebral bodies so that main body10 is disposed in disc space DS (FIG. 2), with upper surface 25 engagingthe lower endplate of the upper vertebral body and lower surface 30engaging the upper endplate of the lower vertebral body, and with thefixed vertical retention plate 140 on proximal end 20 engaging the upperand lower vertebral bodies. Retention plate 35 on distal end 15 isextended away from main body 10, to avoid binding from the upper andlower vertebral bodies, deployed so that it is misaligned to main body10 and retracted using rod 55.

Thus it is understood that the spine is locked in sandwiched relationbetween vertical retention plate 140 on the proximal side and retentionplate 35 on the distal side even though only one incision has been made,said incision being on said proximal side. Retention plate 35 on thedistal side is deployed into position by rotation of rod 55 and noincision is made on said distal side, thereby distinguishing theinvention from prior art implants that require two (2) incisions, i.e.,incisions on both the proximal and the distal side of the spine. Rod 55may be provided with a tool-engageable head to facilitate its rotation.

Spinal fusion implant 5 is sized so that the distance between uppersurface 25 and lower surface 30 is substantially the same as the heightof the disc that the spinal fusion implant replaces, so that the properspacing of the vertebral bodies can be maintained.

Spinal fusion implant 5 is also sized so that it can span cancellousportion CA of vertebral body V, with its proximal and distal endsresting on diametrically opposed portions CO of vertebral body V (FIG.6). As a result, spinal fusion implant 5 supports the affected segmentof the spine and immobilizes the affected segment of the spine, therebyfacilitating fusion between the opposing vertebral bodies.

Apertures 50 of permit the cancellous bone CA of the upper vertebralbody and the cancellous bone CA of the lower vertebral body to grow intospinal fusion implant 5 to further facilitate bone fusion. Apertures 50may be filled with a bone growth promoter.

Spinal fusion implant 5 is inserted into a disc space using a lateralapproach. The lateral approach is preferred because it is familiar tospine surgeons, and also minimizes the possibility of damage to thespinal cord during insertion of the spinal fusion implant.

An instrument is first used to determine the disc plane VP of the discspace which is to receive spinal fusion implant 5. Properly identifyingthe disc plane of the disc space is important because disc plane VP maybe used to identify the proper position for disc space DS to receive thespinal fusion implant.

At least one of the instruments preferably includes a directionalfeature which is used to maintain alignment of the instrumentation withthe vertical plane of the intervertebral joint. By way of example butnot limitation, a directional cannula may include a flat portion and theremaining instruments may include a flat portion on an opposite portionof the instrument, so that the instruments may be inserted through thecannula at zero degrees (0°) or one hundred eighty degrees (180°) only.

After disc space DS has been formed, spinal fusion implant 5 is insertedinto disc space DS so that substantially main body 10 spans the gapbetween the opposing vertebral bodies, with lower surface 30 resting onthe upper endplate of the lower vertebral body and upper surface 25supporting the lower endplate of the upper vertebral body, with verticalretention plate 140 engaged with the upper and lower vertebral bodies.Retention plate 35 then is deployed to the misaligned position andretracted by rod 55 to engage the upper and lower vertebral bodies tolock the upper and lower vertebral bodies against lateral and torsionalmovement, etc. relative to spinal fusion implant 5 and relative to eachother.

Preferably, spinal fusion implant 5 is slightly oversized relative todisc space OS so as to create a press fit. Spinal fusion implant 5provides the stability and strength needed to immobilize the vertebralbodies while fusion occurs. Due to the non-circular cross-section ofsubstantially parallelepiped body 10 and the disposition of the opposingvertebral bodies, spinal fusion implant 5 will hold the opposingvertebral bodies stable relative to one another.

If spinal fusion implant 5 is formed out of a sufficiently strong andrigid material, disc space DS may not need to be pre-formed from thedisc and the opposing vertebral bodies. In this case, the spinal fusionimplant may be simply tapped into place, in much the same manner that apunch is used.

The sixth embodiment is depicted in FIGS. 14-15. It is similar to thefifth embodiment but it lacks spacer 60.

The seventh embodiment is depicted in FIGS. 16-18. In this embodiment,proximal retention plate 140 is permanently mounted in perpendicularrelation to the plane of main body 10, i.e., said proximal retentionplate is not rotatably mounted. Distal retention plate 35 is rotatablymounted on rod 55 because it must be undeployed when device 5 isinserted. Openings 65 are provided to receive screws or other suitablefastening means to enhance the connection between the device and thevertebrae.

FIGS. 19 and 20 depict the eighth embodiment. Proximal retention plate140 in this embodiment is not embedded within main body 10 as depictedin FIGS. 16-18 but is instead secured against rotation bytool-engageable bolts 80 or other suitable fastening means in overlyingrelation to the proximal end of main body 10. Distal retention plate 35is attached to rod 55 and is free to deploy into locking position.

The ninth embodiment is depicted in FIGS. 21-22. As best depicted inFIG. 22, proximal retention plate 140 is integrally formed with theproximal end of main body 10 and thus has a fixed position. Saidproximal retention plate has an upwardly protruding section that extendsabove upper surface 25 and a downwardly protruding section that extendsbelow lower surface 30. Openings 65 are provided to receive screws orother suitable fastening means to enhance the connection between thedevice and the vertebrae.

FIGS. 23-25 depict the tenth embodiment. Protuberances, collectivelydenoted 85, are formed in the respective inboard surfaces of distal andproximal retention plates 35 and 140, respectively. Protuberances 85engage their adjacent vertebrae and thus further secure device 5 againstmovement. The protuberances are disposed within openings 90 (FIG. 25)when the retention plates are not rotated, i.e., coplanar with main body10.

The protrusions collectively denoted 85 are preferably provided onretention plates 35 and 140 respectively to provide an additional meansof affixing spinal fusion implant 5 to upper and lower vertebrae.However, only one (1) protrusion is within the scope of this invention.

Embodiment eleven is depicted in FIG. 26. This embodiment adds arcuaterecesses 95 to accommodate protuberances 85. Distal retention plate 35has been rotated from its coplanar position with main body 10 to itsdepicted position by a counterclockwise rotation and proximal retentionplate 140 has been rotated from its coplanar position with main body 10to its depicted position by a clockwise rotation.

This eleventh embodiment also discloses that the proximal and distalhalves of main body 10 may be formed of two distinct pieces so that saidproximal and distal ends may be spaced apart from one another asdepicted when lengthening of device 5 is required. Main body 10 isdivided into two parts along a parting line that is transverse to alongitudinal axis of symmetry of said main body so that its proximal anddistal ends can be spaced apart from one another as depicted, maintainedin cooperative alignment with one another by central rod 55. The centralrod has a first length substantially equal to the predetermined lengthof the main body and an infinite plurality of second lengths greaterthan said predetermined length. More particularly, the central rod hastwo parts that are screwthreadedly secured to one another so thatrelative rotation between the two parts in a first direction lengthensthe central rod and relative rotation between the two parts in a seconddirection shortens the central rod. The two independently formedsections of the main body are disposed in abutting relation to oneanother when the central rod is at its first length and the twoindependently formed sections of the main body are disposed inlongitudinally spaced apart relation to one another when the central rodis lengthened.

Embodiment twelve is depicted in FIG. 27. This embodiment addsanti-rotation rods 100, parallel to rod 55 and disposed on oppositesides thereof, that interconnect the proximal and distal ends of mainbody 10 to one another and prevent relative rotation therebetween.

FIG. 28 depicts the thirteenth embodiment. This embodiment addsapertures 52 that extend horizontally through main body 10 and which arepreferably in open communication with vertical apertures 50. Likevertical apertures 50, apertures 52 may be filled with bone growthpromoting substance.

The fourteenth embodiment is depicted in FIGS. 29-30. Instead ofanti-retraction teeth 70, the anti-retraction function is performed byprotuberances or spikes, collectively denoted 72, formed in upper andlower surfaces 25 and 30. This embodiment also includes rotatablymounted distal retention plate 140 but no proximal retention plate isprovided. The proximal end 20 of main body 10 is extended as depicted onopposite sides thereof and said extensions are covered with saidprotuberances 72 to provide traction. Such extensions are also providedat distal end 15.

This fourteenth embodiment also includes short adjustment shaft 195 withkey 200 used to restrict deployment motion. Key 200 is received withinnon-circular port 190. The key way is the larger diameter portion ofnon-circular port 190 that allows the key to rotate over a fixed angle.

This embodiment further includes key way port 190 (FIG. 29) on proximalend 20 which enables insertion of an adjustment device, not depicted,for distal retention plate 35. Key way port 190 could also be used tohold a proximal retention plate. A proximal retention plate can beattached to the device after the distal retention plate is deployed. Inall embodiments that depict distal retention plate only (FIGS. 3, 8, 29and 34), a proximal retention plate may be attached to the device afterthe distal retention plate is deployed to enhance stability.

The fifteenth embodiment is depicted in FIG. 31. This embodiment issimilar to embodiment number fourteen but this embodiment includesdistal and proximal retention plates 35 and 140, respectively. Theretention plates are mounted to cylindrical shafts 195. No anti-rotationkey is provided on these shafts but such keys and associated keywaysformed in main body 10 are within the scope of this invention.

The sixteenth embodiment is disclosed in FIGS. 32 and 33. Each distaland proximal retention plate is provided in two (2) separate parts 35 a,35 b, and 140 a, 140 b, respectively. Each separate part is pivotallymounted for rotation from the undeployed positions of FIG. 32 to thedeployed position of FIG. 33. The retention plates that are deployedabove top surface 25 of main body 10 engage the superior vertebral bodyand the retention plates that are deployed below bottom surface 30 ofmain body 10 engage the inferior vertebral body.

As in all embodiments that include rotatable retention plates, saidretention plates are initially in an undeployed, co-planar position withmain body 10 when said main body 10 is inserted between adjacentvertebral bodies. The retention plates and subsequently rotated aftermain body 10 is inserted between adjacent vertebral bodies.

FIGS. 34 and 35 depict the seventeenth embodiment. This embodimentincludes hinged retention plate 35 on distal end 15 of main body 10.

FIG. 35 is a side view depicting retention plate 35 in a deployedposition, flush against main body 10. Retention plate may be attached tomain body 10 by rod 55, short shaft 195, or by spacers 60. The hingesare denoted 205.

The present invention provides a new and improved spinal fusion implantfor facilitating vertebral body fusion. This innovative spinal fusionimplant is able to withstand greater forces, prohibit motion in alldirections and drastically reduce the risk of implant failure. The novelspinal fusion implant also eliminates the possibility of slippage duringspinal motion, greatly improves vertebral body stability and promotesbetter inter-vertebral body fusion.

Numerous advantages are achieved by the present invention. Among otherthings, the present invention provides a fast, simple and easilyreproduced approach for effecting spinal fusion. It also providessufficient stabilization, where posterior plate or pedicle screws arenot needed. Moreover, the present invention may be practiced using aminimally-invasive procedure or open surgical procedure.

While spinal fusion implant 5 has been disclosed in the context offusing an intervertebral joint, it may also be used to stabilize andfuse any joint having anatomy similar to the intervertebral joint, i.e.,a pair of opposing bony surfaces defining a gap therebetween, with thestabilizer of the fusion implant being sized to be positioned within thegap. By way of example but not limitation, the fusion implant may beused in small joints such as in the finger, toe, etc.

It will thus be seen that the objects set forth above, and those madeapparent from the foregoing disclosure, are efficiently attained andsince certain changes may be made in the above construction withoutdeparting from the scope of the invention, it is intended that allmatters contained in the foregoing disclosure or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention that, as amatter of language, might be said to fall therebetween.

1. A spinal fusion implant comprising: a main body having a distal end,a proximal end, a superior surface extending between said distal end andsaid proximal end, said superior surface being configured to engage afirst vertebral body of a spinal joint, and an inferior surfaceextending between said distal end and said proximal end, said inferiorsurface being configured to engage a second vertebral body of a spinaljoint; a distal retention plate rotatably disposed adjacent to saiddistal end of said main body, said distal retention plate having (i) afirst position wherein said distal retention plate is located withinaxial projections of said superior and inferior surfaces of said mainbody, and (ii) a second position wherein said distal retention plateextends beyond axial projections of said superior and inferior surfacesof said main body; wherein said distance between said distal end of saidmain body and the proximal end of said main body is approximately thesame as the distance between opposing cortical distal and proximal facesof the first and second vertebral bodies, wherein the opposing corticaldistal and proximal faces are disposed normal to said superior surfaceof said main body and said inferior surface of said main body; whereinsaid distal retention plate is in said first position when said mainbody is inserted into the spinal joint between the first vertebral bodyand the second vertebral body; and wherein said distal retention plateis in said second position after said main body is inserted into thespinal joint between the first vertebral body and the second vertebralbody, and said distal retention plate is disposed in said secondposition after said insertion such that said distal retention plateengages the opposing cortical distal faces of the first vertebral bodyand the second vertebral body, whereby to inhibit retraction of saidmain body and hold said spinal fusion implant and adjacent vertebralbodies in a stable relationship relative to one another.
 2. The spinalfusion implant according to claim 1, further comprising a spacerdisposed between said distal end of said main body and said distalretention plate.
 3. The spinal fusion implant according to claim 1,wherein said distal retention plate comprises a roughened inboardsurface.
 4. The spinal fusion implant according to claim 1, furthercomprising a proximal retention plate disposed adjacent to said proximalend of said main body, wherein at least a portion of said proximalretention plate extends beyond axial projections of at least one of saidsuperior surface and said inferior surface of said main body, such thatsaid proximal retention plate limits travel of said main body as saidmain body is inserted between said adjacent vertebral bodies.
 5. Thespinal fusion implant according to claim 4, wherein said proximalretention plate is rotatably mounted to said proximal end of said mainbody.
 6. (canceled)
 7. The spinal fusion implant according to claim 4,wherein said proximal retention plate comprises a roughened inboardsurface.
 8. The spinal fusion implant according to claim 1, wherein saidmain body is substantially solid.
 9. (canceled)
 10. (canceled)
 11. Thespinal fusion implant according to claim 1, wherein said main bodycomprises at least one opening formed therein to permit bone in-growth.12. The spinal fusion implant according to claim 11, wherein said atleast one opening extends completely through said main body from saidsuperior surface of said main body to said inferior surface of said mainbody.
 13. The spinal fusion implant according to claim 11, wherein abone growth promoter is disposed in said at least one opening.
 14. Thespinal fusion implant according to claim 1, wherein at least one of saidsuperior surface of said main body and said inferior surface of saidmain body comprises at least one protrusion configured to inhibitretraction of said main body when said main body is positioned betweenadjacent vertebral bodies.
 15. (canceled)
 16. The spinal fusion implantaccording to claim 1, wherein said distal retention plate comprises atleast one protrusion extending distally from an inboard surface of saidproximal retention plate, and said proximal end of said main bodycomprises at least one groove; wherein said at least one groove receivessaid at least one protrusion when said distal retention plate isrotated.
 17. The spinal fusion implant according to claim 1, whereinsaid proximal retention plate comprises at least one protrusionextending distally from an inboard surface of said proximal retentionplate, and said proximal end of said main body comprises at least onegroove; wherein said at least one groove receives said at least oneprotrusion when said proximal retention plate is rotated.
 18. The spinalfusion implant according to claim 1, wherein said distal retention platecomprises two separate parts, wherein each of said two separate parts isrotatably secured to said distal end of said main body, and furtherwherein said two separate parts are rotatable in opposite directionsrelative to one another.
 19. The spinal fusion implant according toclaim 4, wherein said proximal retention plate comprises two separateparts, wherein each of said two separate parts is rotatably secured tosaid proximal end of said main body, and further wherein said twoseparate parts are rotatable in opposite directions relative to oneanother.
 20. The spinal fusion implant of claim 1, wherein said mainbody comprises two independently formed sections divided from oneanother along a parting line that is transverse to a longitudinal axisof said main body extending between said distal end and said proximalend of said main body, said parting line being disposed substantiallymid-length of said main body such that said two independently formedsections have a substantially common length.
 21. The spinal fusionimplant of claim 20, further comprising: a longitudinally-extending boreformed in said two independently formed sections of said main body, saidlongitudinally-extending bore being disposed in substantial coincidencewith a longitudinal axis of symmetry of said main body; a central roddisposed in said longitudinally-extending bore; said central rod havinga first length substantially equal to said distance between said distalend and said proximal end of said main body; said central rod comprisinghaving two parts that are screwthreadedly secured to one another suchthat relative rotation between said two parts in a first directionlengthens said central rod, and relative rotation between said two partsin a second, opposite direction shortens said central rod; wherein saidtwo independently formed sections of said main body are disposed inabutting relation to one another when said central rod is at its firstlength; and said two independently formed sections of said main bodybeing disposed in longitudinally spaced apart relation to one anotherwhen said central rod is lengthened.
 22. The spinal fusion implantaccording to claim 21, further comprising a pair of substantiallyparallel anti-rotation rods disposed parallel to said central rod onopposite sides thereof; wherein said anti-rotation rods connect saidproximal end of said main body to said distal end of said main body,whereby to prevent relative rotation therebetween. 23-25. (canceled) 26.The spinal fusion implant according to claim 1, wherein said distal endof said main body is tapered relative to said main body such that saiddistal end of said main body is not as thick as a central region of saidmain body disposed between said distal end of said main body and saidproximal end of said main body.
 27. (canceled)
 28. A method forpreventing movement of a first vertebral body relative to a secondvertebral body, said method comprising: providing a spinal fusionimplant, comprising: a main body having a distal end, a proximal end, asuperior surface extending between said distal end and said proximalend, said superior surface being configured to engage a first vertebralbody of a spinal joint, and an inferior surface extending between saiddistal end and said proximal end, said inferior surface being configuredto engage a second vertebral body of a spinal joint; a distal retentionplate rotatably disposed adjacent to said distal end of said main body,said distal retention plate having (i) a first position wherein saiddistal retention plate is located within axial projections of saidsuperior and inferior surfaces of said main body, and (ii) a secondposition wherein said distal retention plate extends beyond axialprojections of said superior and inferior surfaces of said main body;wherein said distance between said distal end of said main body and theproximal end of said main body is approximately the same as the distancebetween opposing cortical distal and proximal faces of the first andsecond vertebral bodies, wherein the opposing cortical distal andproximal faces are disposed normal to said superior surface of said mainbody and said inferior surface of said main body; wherein said distalretention plate is in said first position when said main body isinserted into the spinal joint between the first vertebral body and thesecond vertebral body; and wherein said distal retention plate is insaid second position after said main body is inserted into the spinaljoint between the first vertebral body and the second vertebral body,and said distal retention plate is disposed in said second positionafter said insertion, such that said distal retention plate engages theopposing cortical distal faces of the first vertebral body and thesecond vertebral body, whereby to inhibit retraction of said main bodyand hold said spinal fusion implant and adjacent vertebral bodies in astable relationship relative to one another; while said distal retentionplate is disposed in said first position, inserting said main body intothe spinal joint between the first vertebral body and the secondvertebral body; rotating said distal retention plate to said second,rotated position, such that said distal retention plate engages theopposing cortical distal face of the first vertebral body and the secondvertebral body.